package wire

import (
	"fmt"
	"io"
	
	"github.com/p9c/p9/pkg/chainhash"
)

// MaxBlockLocatorsPerMsg is the maximum number of block locator hashes allowed per message.
const MaxBlockLocatorsPerMsg = 500

// MsgGetBlocks implements the Message interface and represents a bitcoin
// getblocks message. It is used to request a list of blocks starting after the
// last known hash in the slice of block locator hashes. The list is returned
// via an inv message (MsgInv) and is limited by a specific hash to stop at or
// the maximum number of blocks per message, which is currently 500.
//
// The HashStop field to the hash at which to stop and use AddBlockLocatorHash
// to podbuild up the list of block locator hashes. The algorithm for building the
// block locator hashes should be to add the hashes in reverse order until you
// reach the genesis block. In order to keep the list of locator hashes to a
// reasonable number of entries, first add the most recent 10 block hashes, then
// double the step each loop iteration to decrease the number of hashes the
// further away from head and closer to the genesis block you get.
type MsgGetBlocks struct {
	ProtocolVersion    uint32
	BlockLocatorHashes []*chainhash.Hash
	HashStop           chainhash.Hash
}

// AddBlockLocatorHash adds a new block locator hash to the message.
func (msg *MsgGetBlocks) AddBlockLocatorHash(hash *chainhash.Hash) (e error) {
	if len(msg.BlockLocatorHashes)+1 > MaxBlockLocatorsPerMsg {
		str := fmt.Sprintf(
			"too many block locator hashes for message [max %v]",
			MaxBlockLocatorsPerMsg,
		)
		return messageError("MsgGetBlocks.AddBlockLocatorHash", str)
	}
	msg.BlockLocatorHashes = append(msg.BlockLocatorHashes, hash)
	return nil
}

// BtcDecode decodes r using the bitcoin protocol encoding into the receive r. This is part of the Message interface
// implementation.
func (msg *MsgGetBlocks) BtcDecode(r io.Reader, pver uint32, enc MessageEncoding) (e error) {
	if e = readElement(r, &msg.ProtocolVersion); E.Chk(e) {
		return
	}
	// Read num block locator hashes and limit to max.
	var count uint64
	if count, e = ReadVarInt(r, pver); E.Chk(e) {
		return
	}
	if count > MaxBlockLocatorsPerMsg {
		str := fmt.Sprintf(
			"too many block locator hashes for message [count %v, max %v]", count, MaxBlockLocatorsPerMsg,
		)
		return messageError("MsgGetBlocks.BtcDecode", str)
	}
	// Create a contiguous slice of hashes to deserialize into in order to reduce
	// the number of allocations.
	locatorHashes := make([]chainhash.Hash, count)
	msg.BlockLocatorHashes = make([]*chainhash.Hash, 0, count)
	for i := uint64(0); i < count; i++ {
		hash := &locatorHashes[i]
		if e = readElement(r, hash); E.Chk(e) {
			return
		}
		if e = msg.AddBlockLocatorHash(hash); E.Chk(e) {
		}
	}
	return readElement(r, &msg.HashStop)
}

// BtcEncode encodes the receiver to w using the bitcoin protocol encoding. This is part of the Message interface
// implementation.
func (msg *MsgGetBlocks) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) (e error) {
	count := len(msg.BlockLocatorHashes)
	if count > MaxBlockLocatorsPerMsg {
		str := fmt.Sprintf(
			"too many block locator hashes for message "+
				"[count %v, max %v]", count, MaxBlockLocatorsPerMsg,
		)
		return messageError("MsgGetBlocks.BtcEncode", str)
	}
	if e = writeElement(w, msg.ProtocolVersion); E.Chk(e) {
		
		return
	}
	if e = WriteVarInt(w, pver, uint64(count)); E.Chk(e) {
		return
	}
	for _, hash := range msg.BlockLocatorHashes {
		if e = writeElement(w, hash); E.Chk(e) {
			return
		}
	}
	return writeElement(w, &msg.HashStop)
}

// Command returns the protocol command string for the message.  This is part of the Message interface implementation.
func (msg *MsgGetBlocks) Command() string {
	return CmdGetBlocks
}

// MaxPayloadLength returns the maximum length the payload can be for the receiver. This is part of the Message
// interface implementation.
func (msg *MsgGetBlocks) MaxPayloadLength(pver uint32) uint32 {
	// Protocol version 4 bytes + num hashes (varInt) + max block locator hashes + hash stop.
	return 4 + MaxVarIntPayload + (MaxBlockLocatorsPerMsg * chainhash.HashSize) + chainhash.HashSize
}

// NewMsgGetBlocks returns a new bitcoin getblocks message that conforms to the Message interface using the passed
// parameters and defaults for the remaining fields.
func NewMsgGetBlocks(hashStop *chainhash.Hash) *MsgGetBlocks {
	return &MsgGetBlocks{
		ProtocolVersion:    ProtocolVersion,
		BlockLocatorHashes: make([]*chainhash.Hash, 0, MaxBlockLocatorsPerMsg),
		HashStop:           *hashStop,
	}
}